1. Field of the Invention
This invention relates to a method or computational model for solving a set of ordinary differential equations that are reduced from and represent an approximation of a more complex and complete set of governing partial differential equations, thereby allowing computational modeling of complex physical processes at work in turbulent flames.
2. Description of Prior Art
Flame properties typically of interest, particularly when considering development of turbulent flames producing low nitrogen oxides (NO.sub.x) emissions for natural gas burning applications in industry and utilities, include: overall pollutant emission levels, of which NO.sub.x are one primary concern; flame liftoff and blowout stability characteristics; heat release patterns within flames; and even flame geometries. Aside from such global flame characteristics, detailed information available from a combustion code, such as identification of areas or zones of high pollutant formation rates within the flame can be used as a tool for designing low NO.sub.x flames.
Computational requirements for numerically solving the complete governing equations that determine fluid motion and reaction chemistry in turbulent flames far exceed the capabilities of most modern computers. For this reason, conventional numerical calculations of combustion characteristics in turbulent flames are based on time-averaged versions of the governing equations, the mathematical nature of which requires that turbulence modeling be incorporated into such calculations to solve the equations. Many conventional turbulence models function under an assumption that mixing between fuel and oxidant in turbulent flames is a gradient transport process. However, such conventional turbulent flame codes based upon such assumptions have proven unreliable for predicting many important and sensitive combustion phenomena resulting from various designs of natural gas burning equipment, including crucial flame properties such as in-flame NO.sub.x levels and flame stability limits. Such conventional combustion codes are of limited utility for exploring large design changes for achieving desired turbulent flame properties, such as NO.sub.x reduction, increased flame stability, and increased flame radiation.
Strict requirements for low NO.sub.x emission levels in gas burning applications suggest that significant departures from conventional designs are necessary to meet these stringent requirements. It will be necessary to analyze complex and detailed physical processes governing combustion and NO.sub.x formation in turbulent flames.